FLOOD01357

• Designation Number: 107
• County: Jefferson
• Community: Unincorporated Jefferson County
• Stream Name: Green Mountain Area
• Title: FHAD - Green Mountain Area
• Date: 4/1/1978
• Designation Date: 7/11/1978
• Floodplain - Doc Type: Floodplain Report/Masterplan

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The flood hazards in this reach are erosion, debris removal and
cleanup, and interrupted traffic and services, and a low to moderate
life hazard due to the recreational use of the area inundated.

4. Station 21+00 to 0+00, 1-70 to Confluence (Sheet 37)

3. Station 47+00 to 21+00, 6th Avenue to 1-70 (Sheets 36 & 37)
The channel in this reach varies from a broad V-shaped section
to a trapezoidal section, with an average slope of about 3.2%, The channel
area has been encroached upon by the low density residential development
in the reach and as a result has minor to appreciable amounts of
obstructions. Drainageway G-2 is tributary to the channel in this reach
just upstream of Colfax Avenue (26+70).
The channel is crossed by 1-70 and Colfax Avenue and by 7th Avenue.
Above 7th Avenue the flood plain is generally contained within the channel
with some flooding of Kendrick Street. Below 7th Avenue, the flood plain
includes a wide expanse of shallow flooding caused by the limited culvert
capacity at 7th Avenue and the channel encroachments on Drainageway G3.
The 100 year flow overtops Colfax Avenue and floods the adjacent commercial
areas. In addition, the flow splitting that occurs upstream of 6th Avenue,
due to the limited culvert capacity, causes shallow flooding in the area
between Indiana Street, Isabell Street, and Joyce Street from 6th Avenue to
Colfax, The flood plain which would result from 100 year frequency culvert
improvements at 6th Avenue is also shown on the drawing to illustrate the
downstream effect, The flood hazards in the reach consist of erosion,
debris removal and cleanup, interrupted traffic and services, structural
and content damage in the residential area, content and inventory damage
in the commercial area, and a low to moderate life hazard due to the large
inundated residential area.

The drainageway in this reach consists of a trapezoidal main
channel and a broad overbank area, with an average slope of about 2.2%,
The channel traverses through Camp George West and the mobile home park
south of Golden Road. The channel is crossed by the Welch Ditch in a
concrete flume (opening underneath is completely silted in), Camp George
Road, Golden Road (culvert currently under construction), and a service
road in the mobile home park. The flood plain can be contained within the
main channel, except that a large portion of the flows split off at the
service road in the mobile home park causing extensive shallow flooding.
The flood hazards in the reach consist of erosion, debris removal
and cleaning, interrupted traffic and services, structural and content
damage to the mobile homes, damage to the ditch, and a moderate life
hazard due to the high velocity deep channel flow.
5. Station 36+00 to 0+00, U stream Stud Limits to Draina ewa G
Confluence Sheets 38 & 39
The channel in this reach (designated Drainageway G-1) varies
from a narrow V-shaped section in the lower and extreme upper reach to a
broad shallow swale area in the middle reach. The channel which has an
average slope of 8%, combines with Drainageway G just above the south
boundary of the Jefferson County Fairgrounds, The channel passes through
a small erosion control pond constructed without a spillway. The flood
plain is generally contained within the channel area with high velocity
flow.

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